So, it seems a very popular pastime among authors these days is to make up a list of ten rules of writing. Reading over some of them from several of our more popular and successful writers is instructive, if for no other reason than to observe how absorbed most of them are in their own craft. That is to say, it's interesting to see how closely each of their ten specific rules relates and applies directly to their style and tone, in some cases to the exclusion of how others are writing today, or yesterday. An author who prefers sparse dialogue to descriptive setting will offer a rule telling you to keep your narrative to a minimum and let the characters reveal themselves by what they say. Less trees, more talk.

Try to avoid having your characters converse in a white space with nothing but their voices on the page. Setting matters. Don't go overboard, but let your readers see where your characters are interacting.
If you're writing literary fiction, have something actually happen, preferably melodramatic. Interior conflict only goes so far in carrying a story forward. On the other hand, genre writers ought to avoid having their characters behave like robots. Plot driven fiction does not preclude interior reflection or character development.
Write what most appeals to you, regardless of publishing trends. Don't choose a story because you think it's what's selling; choose one that fascinates and inspires you.
Use the English language! Hemingway's relative minimalism is not the last word on style. Some writers may preach that less is more, but that's simply personal preference. Elmore Leonard is not a better writer or stylist than James Lee Burke, nor is Hemingway better than Faulkner. They're just different.
In that same vein, try to avoid using "said" in every instance of dialogue attributions. Eighty percent of the time will be sufficient! In other instances, no, there is nothing wrong with using "remarked," "noted," "observed," "suggested," "offered," "explained," "complained," etc. It just makes your text more lively, more colorful, subtly more interesting. It's wallpaper, but it will be noticeable.
Read, read, read. It seems to be the silliest, most obvious advice to give writers, but over my years teaching at the Santa Barbara Writers Conference, I couldn't count the number of times I've heard writers say they're too busy writing to read books. Sad, but true. Or those same writers will only read in their genre or field of interest. Many will read only fiction. Too bad, again, because reading widely in fiction, non-fiction, and poetry offers the opportunity of exploring not only intellectual opportunities, but also discovering different styles and narratives, as well. That's never a bad thing.
Try writing in different points of view: first person, third person, and second person, just simply to see how it's done, how it feels. Maybe you'll find a voice more appropriate and fitting better to what you're working on. Also, begin casting a careful eye on what's possible within those narrative points of view. For instance, we've become so used the idea of third person omniscient narrative within a form of stream of consciousness that we've forgotten how to tell a story about the characters, rather than from within them. Think Grimm's fairy tales! Also, consider the true flexibility offered by a first person, with that immediate character serving as the omniscient narrator. Too often, first person is rejected because the writer believes his narrator must be present whenever the action is occurring. Not so! If the narrator is telling the entire book, he can be in or out of the action as often as he chooses.
Get used to spelling and grammar being an important part of writing. Don't imagine that your agent or editor is going to do the irritating work of giving your story a makeover by correcting bad grammar and misspellings. Don't rely slavishly on spell check. Look up words you're unsure of. Consult grammar guides on the proper use of semi-colons. Learn how words are spelled. Learn how to punctuate sentences. Doing so will make the architecture of your pages elegant and clean.
Find people to read your work who are reliable enough to care about your work and who understand what you're trying to accomplish. Fewer readers are preferable to many. One well-read mentor will be more helpful than half a dozen friends or family members. If possible, have different people read for different reasons. For instance, I've always tried to find readers interested in either story or style or grammar, or pacing. I look for different responses from each. Workshops can be helpful if you trust the readers, but beware of art-by-committee. You cannot go into a workshop having no idea of the worth or quality of your writing. Otherwise the blizzard of comments and suggestions will be confusing and counter productive. Trust in your own opinion best of all. No one will care about your work more than you will.
Make writing your life, not just a passing fancy. Don't imagine that publishing a novel will make you rich and famous. Maybe it will, but probably it won't. Don't see writing as a career change. Don't give yourself six months, a year, two years to make it as a writer. Think instead that once you put words on a page, you are a writer, and this is something that will fascinate, frustrate and fulfill your soul for the rest of your life. Don't believe in writer's block. There's no such thing. My dad told me that only amateurs get writer's block; professional's can't afford it. I'd add to that only the dilettante gets writer's block; the passionate are never dissuaded. Believe in the magic of the written word. And put more words on paper!